I used a Kuryakyn universal bar mount and a Monaco aluminum case. Took a tiny bit of fitting to mount the aluminum case to the Kury mount plate but works great. Snaps shut so not too worried about it opening up and dropping the phone but sometimes add a band/strap to keep it from opening just in case.
Mine is for a Blackberry but they make the case for iPhones as well.
http://newpdacases.com/index.php?main_page=product_info&cPath=148_165&products_id=938
